A switching regulator is a circuit that uses a power switch, an inductor, and a diode to transfer energy from input to output. In contrast to linear regulators that use a resistive voltage drop to regulate the voltage and lose power in the form of heat a switching regulator does not have a voltage drop and an associated current but instead the current is 90 degree out of phase with the voltage. Due to this, the energy is stored and can be recovered in the discharge phase of the switching cycle. In the art several types of switching regulators exist dependent on how the switching circuit is arranged, for example step-down (buck), step-up (boost) or inverter (flyback). The switch can be controlled by a PWM signal with duty ratio D that represents the on state during a PWM period. The output voltage is dependent on the duty ratio D and, hence, can be controlled by a controller which consists of an analog-to-digital-converter (ADC), a discrete-time control law, and a digital PWM (DPWM) module. The ADC samples and quantizes the regulated signal, the output voltage error that is the difference between the output voltage and an output voltage reference. The control law computes the digital duty ratio command D based on the quantized output voltage error. The control law is a given by a PID control law which is configured by a set of PID coefficients, the set comprising the proportional gain Kp, the integral gain Ki and the differential gain Kd and the time delay Td. The digital PWM modulator takes D as input, and outputs a PWM waveform with the commanded duty ratio D at a switching frequency. The PWM waveform has finite time resolution. The sensing and the quantization of other signals such as the load can be added depending on the application and the specific control law used.
In case a load transient occurs, for example if the output load is reduced leading to an output increase from level A to level B, the duty ratio of the PWM signal has to be increased for a short period of time until the average inductor current has reached the new level B. Once, the average inductor current has reached the new level B, the PWM duty ratio can be reduced again to a slightly higher value.